A data acquisition system may be used to obtain, and possibly record, information about an environment. Information obtained from the environment by the data acquisition system may be used to adjust a system operating in or controlling that environment. Typically, one or more sensors are used to sense a condition of the environment. A signal generated by the one or more sensors may need to be amplified and/or filtered by the data acquisition system for proper operation.
In some environments, information from a large number of sensors is desirable. Each sensor typically requires amplification and/or filtering. As the number of sensors increases, so does the required number of amplifier circuits and/or filter circuits. Eventually, a design tradeoff may be required between a physical size of the data acquisition system and a number of amplifier circuits, a complexity of a design of the amplifier circuits, a number of filter circuits, and a complexity of a design of the filter circuits.
The number of amplifier circuits and/or the number of filter circuits may be shared by several sensors at the expense of reducing a speed and/or an availability at which a particular sensor signal may be acquired. The complexity of the design of the amplifier circuits and/or filter circuits may be limited such that more amplifier circuits and/or filter circuits fit within a monolithic integrated circuit and/or the data acquisition system. Additionally, one or more multiplexers may be used to select between several amplifier circuits and/or filter circuits in a data acquisition system.
FIG. 1 shows a schematic diagram of an typical data acquisition system (100). The exemplary data acquisition system (100) includes a plurality of sensor input signal lines (VIN1, VIN2, VIN3P, VIN3N, VIN4P, VIN4N). The sensor input signal lines (VIN1, VIN2) are single ended sensor input signal lines. The sensor input signal lines (VIN3P, VIN3N, VIN4P, VIN4N) are differential sensor input signal lines. The sensor input signal lines VIN3P and VIN3N are positive and negative sensor input signal lines, respectively, from a sensor. The sensor input signal lines VIN4P and VIN4N are positive and negative sensor input signal lines, respectively, from another sensor.
The plurality of sensor input signal lines (VIN1, VIN2, VIN3P, VIN3N, VIN4P, VIN4N) are amplified by amplifier circuits (102, 104, 106, 108). Each single ended sensor input signal line (VIN1, VIN2) is amplified by an amplifier circuit (102, 104, respectively). Each differential sensor input signal line (VIN3P and VIN3N, VIN4P and VIN4N) is amplified by a differential amplifier circuit (106, 108, respectively). An output signal line (103, 105, 107, 109) from each amplifier circuit (102, 104, 106, 108) is received by a multiplexer (110). The multiplexer (110) selects one of the output signal lines (103, 105, 107, 109) to be received by a filter circuit (112). The filter circuit (112) filters the amplified sensor input signal line selected by the multiplexer (110) and outputs a signal on a VOUT signal line.
The arrangement of the data acquisition system (100) allows multiple sensor input signal lines (VIN1, VIN2, VIN3P, VIN3N, VIN4P, VIN4N) to be received and allows several different types of input signal lines (i.e., single ended and differential) to be received. In this example, a design tradeoff has been made to favor the number and types of input signal lines by reducing the number of filter circuits (112).
When a signal from a particular sensor input signal line is desired, a delay may result because the multiplexer (110) may need to select a different output signal line (103, 105, 107, or 109) and the filter circuit (112) may need to settle before an accurate signal is output on the VOUT signal line. Also, only one sensor input signal line(s), or channel, may be output at any given time.
With respect to a design of the data acquisition system (100), the output signal lines (103, 105, 107, 109) are all routed to the multiplexer (110). The routing may require hand layout and routing because an analog signal may be susceptible to noise created by adjacent signal lines in the routing. Also, if the data acquisition system (100) is disposed on a monolithic integrated circuit, and additional monolithic integrated circuits are added, more channels may be amplified and filtered; however, additional circuitry, external of the monolithic integrated circuits, may be required to acquire the signals from the plurality of VOUT signal lines.